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Introduction

Obesity is an epidemic in the industrialized world and is associated with high blood pressure, high cholesterol, and other problems that put people at risk for heart attacks, strokes, and other adverse consequences. More and more research is being focused on obesity. At the core of the problem is a simple excess in calorie balance. We eat more calories than we burn, and we store those excess calories as fat. However, looking at the problems as a whole, several other factors come into play. For example, an individual’s genetic make-up can predispose him or her to being overweight.

The term infectobesity refers to the theory that an infection of some sort can alter our biology and cause us to put on excess pounds. At first, this may just seem like another made up excuse for those who have been unsuccessful in losing weight. However, there is a body of scientific research that suggests this is a very real possibility. Most of this research is focused on viruses. In animal studies, there are definite obesity virus candidates. This has led scientists to search for a human fat virus. So far, there are two that have studies associating them with increased body fat.

SMAM-1

Although SMAM-1 is a bird virus, it has the ability to infect humans. In studies done on chickens, infection with SMAM-1 caused an increase in their body fat. This happened despite there being an equal amount of food intake between infected and uninfected chickens. The livers of the infected chickens also became enlarged and saturated with high levels of triglycerides. SMAM-1 was the first virus studied in humans as an obesity virus. Researchers checked people’s blood for antibodies to the SMAM-1 virus. Once a person has been exposed to an infection, his or her immune system generally starts producing antibodies to that infection. People who were antibody positive were about 30 lbs heavier than those who were antibody negative. An unexpected effect was that in both the chickens and people in these studies who had been exposed to SMAM-1 cholesterol levels were decreased.

Human Adenovirus 36

The second obesity virus is Human Adenovirus 36 (Ad-36). Adenoviruses generally cause respiratory tract infections, conjunctivitis (pink eye), and a few other types of infections. Again studies were done looking for people who had antibodies to the obesity virus. More obese than lean people were found to be antibody positive, and the BMIs of those exposed to Ad-36 were about 9 points higher than the non-exposed individuals. There are several types of antibodies made by our immune system. One type, IgM, is produced in response to initial exposure to a pathogen. Another, IgG, is made after the initial infection and helps to make us immune to that pathogen later. Several people who had antibodies to Ad-36 produced the IgG type. This means that even past exposure without any active infection still led to obesity. It was also noted that those who were exposed to Ad-36 had better cholesterol levels, just like with SMAM-1.

More research has been done on Ad-36 than SMAM-1, resulting in a more detailed understanding of how this virus causes people to be overweight. Studies have been done on a type of stem cell that can potentially develop into adipose tissue (i.e. fat cells). In the presence of Ad-36, these stem cells are signaled to develop into adipose tissue. It appears that the virus activates a particular genetic sequence called the E4 open reading frame-1 (E4 orf-1). Once this gene is turned on, these stem cells head down the path of becoming fat cells, even if our bodies never intended them to become adipose tissue.

The Cholesterol Paradox

One of the more surprising aspects of obesity viruses is that even though they cause increased body fat, they seem to cause improved cholesterol profiles. There are two possibilities as to how this happens. First, because there are now more fat cells present after infection, they can store cholesterol in the adipose tissue rather than have it circulating in the blood. When blood-work is done for cholesterol, it would then appear as if the person has lower cholesterol levels. Although total body cholesterol levels have not changed, it would still be beneficial to have the cholesterol tucked away inside fat cells rather than circulating through the body where it can cause damage.

The second theory holds that the viruses cause adipose tissue to behave differently by activating certain cellular signal pathways. Some of these pathways are the same ones that are activated by many diabetes medicines, and their side effects can include improved cholesterol levels. This theory is corroborated by the fact that Ad-36 infection leads to improved insulin sensitivity. Insulin is the hormone in our bodies that tells cells to take sugar (glucose) from the blood and use it for energy. Diabetes medicines like metformin turn on the PPARg2 signal pathway which increases the cellular response to insulin. PPARg2 is also activated by Ad-36. Additionally, independent of its insulin sensitizing effects, Ad-36 causes cells to take up more glucose.

Future research

Because of the fact that a virus can contribute to obesity, there may well be a place for the development of an obesity vaccine. Whether or not this vaccine would be worth the expense and any possible side effects would depend on how effective the vaccine would be, how strongly obesity viruses affect one’s body fat, and how prevalent these viruses are in the general population. In the meantime, the work done on the discovery of these viruses, how they lead to being overweight, and how they improve cholesterol profiles gives scientists more information to guide them in developing treatments for obesity and high cholesterol. Even though body weight is best managed by living a healthy lifestyle consisting of diet and exercise, the more we understand this process, the closer we come to additional therapies to combat the obesity epidemic.

Resident Physician in Internal Medicine

The Medical Weight Loss GuideArticle Source:http://www.articlesbase.com/diseases-and-conditions-articles/obesity-virus-1005171.html

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This entry was posted on Thursday, July 2nd, 2009 at 1:28 am and is filed under Common Diseases. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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